Most racket bodies formed from composite materials utilizing, for example, glass fibers and/or carbon fibers, are made by wrapping a web of woven or nonwoven fiber, hereinafter referred to as fabric or mats of fiber, preimpregnatable with a hardenable resin around a mandrel or core constituted of a cellular material (synthetic resin foam or the like) or around an air chamber which is somewhat inflated or under pressure. The web of impregnatable material can extend all along the mandrel or core and consequently, has essentially the same orientation of the fibers where the web forms the arms or branches of the throat piece, any bridge between these branches, the frame portion and, of course, the handle or shaft of the racket body. The latter parts can be formed separately and then joined together with local reinforcement at the junctions.
Another method of forming such rackets is to provide fiber braids around a flexible mandrel which is inflatable or thermally deformable and to impregnate the fiber armature which is thus formed with a resin under pressure. In this case as well the fibers extend over the entire length of the body and the only discontinuities of the structure are constituted by any reinforcements which may locally be required or desirable.
Both of these processes require the use of relatively expensive materials such as carbon fibers, in zones of the racket where they may not be necessary for the required level of strength and the function at the respective portions of the racket. Furthermore, the orientations of the fibers is uniform over the entire length of the body with respect to the axis of the core or mandrel and thus in many parts of the racket, the orientation is not conditioned upon the force distribution required at the particular portion.
Furthermore, when a flexible core or mandrel is used, impregnation of the armature by injection of the synthetic resin under pressure can result in compression of the mandrel under the effect of the resin pressure and this compression tends to increase toward the point of injection which results in a distribution of resin which decreases remotely from this injection point. At part of the racket body, therefore, there is an excess of resin which does not go to improve the strength of the racket but only has an adverse effect upon the weight of the racket body, whereas in other regions, the lack of resin may result in a diminished strength.